Lecture Notes: Elastic and Inelastic Deformation
Objectives
- Understand the difference between elastic and inelastic deformation.
- Calculate the force needed to stretch or compress an object.
- Describe the energy transfers when an elastic object undergoes stretching, compression, or bending.
Key Concepts
Elastic Materials
- Definition: Elastic materials return to their original length or shape when the forces acting on them are removed.
- Examples: Slinky, rubber bands, rubber gloves, eraser, playground surface, tennis ball.
- Forces: Equal in magnitude but opposite in direction, causing balanced forces.
- Elastic Deformation: Changes in length or shape of the object that return to original state when forces are removed.
- Requirement: More than one force must be applied to change an object’s length or shape; a single force would cause movement, not deformation.
Inelastic Materials
- Definition: Inelastic materials do not return to their original length when forces are removed.
- Examples: Certain polymers.
- Inelastic Deformation: Permanent change in shape or length.
Calculating Forces
- Equation: Force (Newtons) = Spring Constant (Newtons/meter) x Extension (meters)
- Note: This equation must be memorized as it is not provided in exams.
Example Problem
- Question: Calculate the force required to extend a spring by 0.04 meters with a spring constant of 200 Newtons/meter.
- Solution:
- Spring constant: 200 N/m
- Extension: 0.04 m
- Calculation: 200 N/m x 0.04 m = 8 Newtons
Application to Compression
- Compression: Use the same equation as for stretching, substituting compression for extension.
Energy Transfers
- Elastic Potential Energy: Stored in the object when stretched or compressed.
- Work Done: Equal to the elastic potential energy stored, assuming no inelastic deformation.
- Further Learning: Elastic potential energy covered in other energy topics.
Next Steps
- Upcoming video will cover the required practical on stretching a spring.
- Additional resources and exercises available in the revision workbook.
Remember to review the video on elastic potential energy for a better understanding of the topic.